In recent years, semiconductor integrated circuits, information storage media such as hard disks, micromachines, and the like have been processed in highly fine patterns. In the fields of processing such workpieces, attention has been attracted to the use of an energetic beam such as a high-density neutral particle beam or a high-density ion beam which is highly linear, i.e., highly directional, and has a relatively large beam diameter. For example, the energetic beam is applied to a workpiece for depositing a film thereon or etching the workpiece.
As beam sources of such energetic beams, there have been used beam generators which generate various kinds of beams including a positive ion beam, a negative ion beam, a neutral particle beam, and a radical beam. The positive ion beam, the negative ion beam, the neutral particle beam, or the radical beam is applied to a desired area of a workpiece from the beam source, for thereby locally depositing a film on the workpiece, etching the workpiece, modifying the surface of the workpiece, or joining or bonding parts of the workpiece.
When charged particles are applied to a workpiece such as an extremely thin silicon oxide film for semiconductor integrated circuits, a dielectric breakdown may be caused on the workpiece. However, a neutral particle beam having no electric charges but having a large translational energy is unlikely to damage a workpiece. Therefore, it has been expected to apply such a neutral particle beam to fine processes.
As a beam source of such a neutral particle beam, there has been known a beam generator which generates a negative ion beam from a plasma and detaches electrons from the negative ion beam by electron impact for thereby neutralizing the negative ion beam. This neutral particle beam generator comprises a neutralizing chamber having a filament therein. Thermoelectrons produced by the filament are trapped in the neutralizing chamber to generate an electron cloud having a high energy. The negative ion beam which has been focused with an electrostatic lens is introduced into the neutralizing chamber and neutralized by detaching electrons while passing through the electron cloud in the neutralizing chamber.
In the case where the negative ions are neutralized by electron impact, it is required to generate a high-density electron cloud in order to obtain a high neutralization efficiency. However, since a high-density electron cloud is generated only in an extremely small space, the beam diameter of the neutral particle beam cannot be made larger.
There has been known another neutral particle beam generator which irradiates photons to a negative ion beam to detach electrons therein for thereby neutralizing the negative ion beam. In this neutral particle beam generator, since a photon energy is larger than an electron detachment energy from the negative ion beam, a high neutralization efficiency can be obtained without dependence upon the energy of the negative ion beam.
In the case where the negative ions are neutralized by application of photons, a large light source and a large optical system are required to make the beam diameter of the neutral particle beam larger, resulting in a larger size of the apparatus. Only a slight part of light emitted from the light source contributes to neutralization, and the rest of light becomes heat loss. In order to obtain a high neutralization efficiency, the light source is required to have a higher fluence. However, the light source having a higher fluence needs a cooling mechanism or the like, resulting in a larger size of apparatus and a higher cost of the equipments.
If a radiation (e.g., an ultraviolet ray) produced by the plasma in the neutral particle beam source is applied to the workpiece, then the radiation adversely affects the workpiece. Thus, it is necessary to shield the workpiece from an adverse radiation (e.g., an ultraviolet ray) emitted from the plasma source.